1. Field of the Invention
The present invention relates to a wavelength stabilization apparatus in a WDM or analog optical communication system, and more particularly, to a wavelength stabilization module having a light-receiving element array which has the dependency of incident angle of a transmission light passing through a F-P filter, to stabilize the wavelength of light output from a laser diode, and a method of manufacturing the same.
2. Description of the Prior Art
In Wavelength Division Multiplexing (WDM) light source module, a multi-functional device has been a world's trend, and the wavelength stabilization function becomes more important in the channel interval of 100 GHz or less. According to this trend, the transceiver module for stabilizing the wavelength becomes one of the most important components in point of view that the structure of the system is simplified so as to increase an economical efficiency and reliability.
Conventionally, to stabilize the wavelength of the transmitted laser beam, various methods such as using a reference absorption gas, a grating, a fiber grating, or a Fabry-Perot (F-P) filter have been used. Among them, efficient and economical means capable of receiving a wide wavelength range in dense WDM (DWDM) having at least several tens of channels is obtained using the F-P filter. The wavelength control precision of wavelength stabilization module developed until recently is approximately 20–50 pm. With this numerical value of the wavelength control precision, the wavelength stabilization module is applicable to the WDM system having channel interval of 100 GHz. However, since most of the modules are external type modules, they have problems in that the systems thereof are complex.
The wavelength stabilization system using the F-P filter has been mainly used in stabilizing the wavelength of a Distributed Feed-Back (DFB) laser diode. As a tuning method for locking the wavelength of the laser diode to the wavelength of an International Telecommunication Union-Telecommunication (ITU-T) grid, several ways have been developed such as the tilting of the angle of an etalon filter, the change of the cavity's length according to the temperature change of the etalon filter, or the change of the mechanical cavity's length according to piezoelectric actuation.
In general, the wavelength of the DFB laser diode is varied by the second method using lie temperature change of the wavelength stabilization module including the etalon filter on a Thermo-Electric Cooler (TEC). The degree of wavelength variation is approximately 0.1 nm/° C., and temperature for stabilizing the wavelength is about 10° C. in 100 GHz-FSR (Free Spectral Range) system. However, when the wavelength tuning function due to the temperature's change is performed in the wavelength stabilization system, the operation condition of the laser diode may be affected, and thus the driving condition of the element becomes very restricted.
In addition, the method of stabilizing the wavelength by tilting the angle of the etalon filter has very high sensitivity in the fine-tilting of the angle. Theoretically, if the wavelength stabilization module is tilted by about 0.01° in an initial state with a rotation of 8° to decrease the reflectivity noise, the wavelength change of about 0.05 nm can be obtained. However, it is difficult for the wavelength stabilization system to be aligned with an accuracy like that, in practical realization, and the yield thereof may be low and the cost thereof is very high.